You cannot migrate a Workspace account into a regular Google account, you're stuck with Workspace forever unless you start over on a brand new account.
And yes I realise that an IoT alarm clock is ridiculous, but that's not the point.
I’m asking because I used to work adjacent to this area, and I know of only a few scenarios where an account becomes a workspace account after being a consumer account.
Workspace accounts come with their own compliance requirements and edge cases that products need to handle, but rather than do that and provide a consistent user experience most product teams don't answer to the relevant PAs and so don't care, and Workspace accounts are a small enough minority of users that nobody has to care.
I've often railed against a particular way of doing product that's really common in our industry, but I suppose it's been a while so I'll do it again:
We have a real problem with metrics-driven product development, where we exclusively care about the 95% use case and actively disdain the 5% use cases.
On paper it makes sense - you direct your energies towards the highest-payback activities. But the problem is that every user falls into some 5% use cases, so a product that is purely made up of 95% use cases ends up becoming a patchwork that is frustrating to every user, somehow.
Rather than "product works great for 95% of users" you get "100% of users cut themselves on some corner of the product".
Hugely frustrating - they penalize their paying customers. Can't attach Nest devices, can't use the YouTube family plan.
"Hey google remind me to call in sick tomorrow"
and it will put an entry into the calendar for me.
But if it is plugged into my car the same request will elicit an
"I'm sorry please talk to your system administrator to get this feature enabled"
This has gone on for years with google assistant and workspace accounts. There is always some random interlock in some byzantine permissions table that get's triggered at the most inconvenient moment and you can't do what yesterday you could do.
I used to pay for Workspace and left because a good chunk of features across all Google products simply didn't work with Workspace accounts, or were held back for a year or more after free Google accounts got them. It's a mess. Then they kept increasing the price for good measure, and there's no off-ramp, if you stop paying then the account is left in a zombie state with even less functionality than a free one until you start paying again.
Do yourself a favour and use Fastmail or Proton or anything else for your vanity domain instead.